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  1. 1. Forces
  2. 2. What is a force? A force is a push or pull from one object to another object Examples: Earth’s gravitational pull on us, you pushing a chair, a table supporting a book
  3. 3. What is a force? All forces have both size and direction The unit of force is the Newton (N) What other concepts have both a size and direction?
  4. 4. Net Forces The net force is the combination all of the forces acting on the object Whenever more than one force act on an object, always sum the forces into a single net force
  5. 5. Forces in the Same Direction When forces act in the same direction, you add the forces together The net force will be in the same direction as the two original forces F1= 5 N Fnet= 8 N F2= 3 N
  6. 6. Forces in the Opposite Direction  When two forces act in opposite directions, you subtract the smaller force from the larger force  The net force will be in the direction of the larger forceF1= 2 N F2= 7 N Fnet= 5 N
  7. 7. Balanced Forces When the sum of the forces acting on an object equals zero, the forces are said to be balanced. Balanced forces are equal in size and opposite in direction
  8. 8. Balanced Forces- Newton’s 1stLaw There is no change in motion when the forces are balanced. A stationary object remains stationary A moving object has constant velocity
  9. 9. Unbalanced Forces When the sum of the forces are non- zero, there are unbalanced forces acting on the object Unbalanced forces produce a change in motion, so they are necessary to cause accelerated motion
  10. 10. The Big Idea Unbalanced forces result in a net force The net force causes the object to accelerate This acceleration can be predicted and described
  11. 11. Force, Mass, andAcceleration An object accelerates when a net force acts upon it The net force is equal to the mass times the acceleration: F = ma This relationship is Newton’s 2nd Law
  12. 12. Force, Mass, and Acceleration  The acceleration of the object depends on both the forces acting on the object and the mass of the object  The net force and acceleration are always in the same direction!!F1= 2 N F2= 7 N Fnet= 5 N a
  13. 13. Example 1 How much force is needed to accelerate a 30 kg scooter at a rate of 1 m/s2? F = ma F = (30 kg) x (1m/s2) F = 30 N
  14. 14. Example 2 How much force is needed to accelerate a 0.5 kg baseball at a rate of 0.04 m/s2? F = ma F = (0.5 kg) x (0.04 m/s2) F = 0.2 N